Q-2 Give a rough estimate (by rounding numbers off to nearest hundreds before calculation) and also a closer estimate (by rounding off to nearest tens):

439+334+4317

1,08,737−47,599

8325−491

4,89,348−48,365

How to Round Numbers

Decide which is the last digit to keep, for example when off to rounding to hundreds the units and tens digit will become zero and the hundreds digit will be kept. So we will be working on the hundreds digits

Leave it the same if the next digit is less than 5 (this is called rounding down)

Increase it by 1 if the next digit is 5 or more (this is called rounding up)

Example 1: To round 764 to the nearest 100

We look at the digit right after the hundred’s digit

Since it is 6 the 7 in the hundreds place is changed to 8 and the answer becomes 800.

Example 2: Round 86 to the nearest 10

We want to keep the "8"

The next digit is "6" which is 5 or more, so increase the "8" by 1 to "9"

Answer: 90. We say that 86 gets "rounded up"

Rounding can be understood with a roller coaster:

4 or Less "Rounded Down" 5 or More Rounded to Next Digit

Numbers 4 or less than 4 are rounded down while numbers 5 or more are rounded up to next digit

Here are 2 examples:

Examples of Rounding With Roller Coaster

Understanding rounding examples with roller coaster.

Solution:

439+334+4317

By rounding off to nearest hundreds

439 rounds off to 400, 334 rounds off to 300 and 4317 rounds off to 4300

The digit we need to look at to decide the value of hundreds digit is underlined

Find the Estimated Value of 439+334+4317 (Nearest Hundredths)

Given the three numbers 439+334+4317, find the estimated sum by first rounding numbers to nearest hundredths

By rounding off to nearest tens

439 rounds off 440, 334 rounds off 330 and 4317 rounds off 4320

The digit we need to look at to decide the value of tens digit is underlined

Find the Estimated Value of 439+334+4317 (Nearest Tens)

Given the three numbers 439+334+4317, find the estimated sum by first rounding numbers to nearest tens

1,08,737−47,599

By rounding off to nearest hundreds

108737 rounds off 108700, 47599 rounds off 47600

The digit we need to look at to decide the value of hundreds digit is underlined

Find the Estimated Value of 108737-47599 (Nearest Hundredths)

Given the three numbers 108737-47599, find the estimated diffrence by first rounding numbers to nearest hundredths

By rounding off to nearest tens

108737 rounds off 108730, 47599 rounds off 47600

The digit we need to look at to decide the value of tens digit is underlined

Find the Estimated Value of 108737-47599 (Nearest Tens)

Given the three numbers 108737-47599, find the estimated sum by first rounding numbers to nearest tens

8325−491

By rounding off to nearest hundreds

8325 rounds off 8300, 491 rounds off 500

The digit we need to look at to decide the value of hundreds digit is underlined

Find the Estimated Value of 8325-491 (Nearest Hundredths)

Given the two numbers 8325-491, find the estimated difference by first rounding numbers to nearest hundredths

By rounding off to nearest tens

8325 rounds off 8330, 491 rounds off 490

The digit we need to look at to decide the value of tens digit is underlined

Find the Estimated Value of 8325-491 (Nearest Tens)

Given the three numbers 8325-491, find the estimated sum by first rounding numbers to nearest tens

4,89,348−48,365

By rounding off to nearest hundreds

489348 rounds off 489300, 48365 rounds off 48400

Find the Estimated Value of 489348-48365 (Nearest Hundredths)

Given the two numbers 489348 & 48365, find the estimated difefrence by first rounding numbers to nearest hundredths

By rounding off to nearest tens

489348 rounds off 489350, 48365 rounds off 48370

Find the Estimated Value of 8330-490 (Nearest Tens)

Given 8325-491, find the estimated difference by first rounding numbers to nearest tens